Comparison of SiNx‐Based Surface Passivation Between Germanium and Silicon

Abstract

Germanium (Ge) has attracted much attention as a promising channel material in nanoscale metal–oxide–semiconductor devices and near‐infrared sensing because of its high carrier mobilities and narrow bandgap, respectively. However, efficient passivation of Ge surfaces has remained challenging. Herein, silicon nitride (SiNx)‐based passivation schemes on Ge surfaces are studied and the observations are compared to Si counterparts. These results show that instead of a high positive charge density (Qtot) that is found in SiNx‐passivated Si samples, similar Ge samples contain a high amount of negative Qtot (in the range of 1012 cm−2). The maximum surface recombination velocity of the samples is shown to reduce by a factor of three in both Si and Ge samples by a post‐deposition anneal at 400 °C. The SiNx‐coated samples are capped with an atomic‐layer‐deposited aluminum oxide (Al2O3) layer, which reduces the midgap interface defect density (Dit) after annealing to 7 × 1010 and 4 × 1011 cm−2 eV−1 in Si and Ge, respectively. Interestingly, while the Al2O3 capping seems to have no impact on Qtot of the Si samples, it turns the stack virtually neutral (∼−1.6 × 1011 cm−2) on Ge. The presented SiNx‐based passivation schemes are promising for optoelectronic devices, where a low Dit and/or a low charge are favored.